In the field of electric power industry providing overhead power lines, an aluminum conductor made from an aluminum-based material is conventionally used because the aluminum conductor is light in weight and excellent in electrical conductivity. In the fields of automobiles, OA equipment, and home electric appliances, a copper conductor made from a copper-based material excellent in electrical conductivity is used for signal lines and electric power lines.
In the field of automobiles, the performance and function of a car have been rapidly improved. Therefore, the number of electric devices, control devices, and other devices to be installed in the car is increasing, and accordingly the number of copper conductors to be used in the car is also increasing.
Recently, attention is focused, especially in the field of automobiles, on an aluminum conductor in which aluminum whose specific gravity is about one third of copper is used for a conductor for the purpose of weight reduction (for information, the density of aluminum is 2.70 g/cm3 and the density of copper is 8.89 g/cm3).
Although a pure aluminum (purity of 99% or more) is used for a conductor having a cross-sectional area of 10 mm2 or more such as a battery cable in the field of automobiles, the pure aluminum is low in strength and inferior in fatigue resistance, and is accordingly difficult to use for an ordinary conductor having a cross-sectional area of 1.5 mm2 or less.
Hence, attempts have been made to improve strength and fatigue resistance of such an aluminum conductor. For example, an automotive electric wire is made from an Al—Mg—Si alloy (see Japanese Patent Application Unexamined Publication No. 2004-134212).
This conductor is prepared by bunching a plurality of aluminum alloy wires which contain 0.6 wt % or less Fe, 0.2 to 1.0 wt % Si, 0.2 to 1.0 wt % Mg, and a remainder including aluminum and an unavoidable impurity, and strength of the aluminum alloy is improved by precipitating Mg2Si and other elements in an Al matrix by heat treatment in the process of producing the conductor.